Two critical hallmarks of chronic Pseudomonas aeruginosa infection in patients with cystic fibrosis (CF) are the appearance of alginate over-producing mucoid colonies and the development of antibiotic resistance. A rapid emergence of antibiotic resistance in P. aeruginosa isolates in CF patients due to in vivo selection of strains that overproduce AmpC [unreadable]-lactamase, an enzyme that hydrolyzes the [unreadable]-lactams, contributes to both morbidity and mortality. Previous studies investigating the regulation of the amp genes in P. aeruginosa using genetic and molecular biological techniques led to the identification of a second [unreadable]-lactamase, PoxB oxacillinase. We showed that the expression of both ampC and poxB are under the control of AmpR, a member of the LysR family of transcriptional regulators. We have demonstrated that AmpR is a global transcriptional regulator which regulates expression of many virulent genes that are important for establishing chronic infections. Our long-term goal is to establish the regulatory circuit that exists between the amp and pox genes and their role in the development of resistance to [unreadable]-lactams and the establishment of chronic infection. To date, we know very little about the molecular mechanisms that govern the expression of pox operon. The experiments proposed in this grant will extend our understanding as they will focus on (1) characterizing the poxAB operon and determining if AmpR regulation is by transcriptional derepression, and (2) determining if expression of the poxAB operon is regulated by a previously uncharacterized two-component system. These analyses will provide invaluable insight into the bacterial adaptation to the onslaught of antibiotics and the immune response. It will likely lead to novel therapeutic approaches in combating the persistent P. aeruginosa infection that ultimately leads to the untimely death of CF patients.